Studies will be conducted using purified transcription termination protein rho from wild-type and rho mutant Escherichia coli to elucidate the biochemical basis of rho defect. We have observed reversibly defective binding of rho-115 to the RNA analog polyC at high temperature. This observation will be extended to other homopolymer synthetic RNA species, and to polymers of complex composition. Initial rate as well as final quantity of bound RNA will be determined. The loss of the binary complex at high temperature in the presence of ADP, ADP, AMP, adenosine, adenine or pyrophosphate will be compared as a function of concentration of these low molecular weight compounds, since the presence of ATP prevents loss of the binary complex. Further, recovery of the rho-polyC complex will be examined in the presence of excess unlabeled polyC, to determine the extent of dissociation of these components. Deletion mutations of the rho gene carried on F'14 or lambda dilv will be sought. The ilv operon of the F'14 plasmid will receive the Tn10 tetracycline-resistance transposon, and deletions that fail to complement rho-115 will be sought among tetracycline-resistant exconjugants. The lambda dilv population will be enriched for rho deletions by previously established methods.